[OFI] ER diagram

Hi,

I wanted to understand the current model better so I've generated ER
diagram from Scott's PR https://github.com/theforeman/staypuft/pull/12.

see http://projects.theforeman.org/projects/ofi/wiki/DB_Model

How to: add gem 'rails-erd' and execute rake erd only='Staypuft::Deployment,Staypuft::DeploymentHostgroup,Staypuft::HostgroupRole,Staypuft::Layout,Staypuft::LayoutRole,Staypuft::Role,Staypuft::RoleClass,Staypuft::RoleService,Staypuft::Service,Staypuft::ServiceClass,Hostgroup,Puppetclass' attributes='foreign_keys,content' orientation=vertical filetype=dot
then dot -Tsvg erd.dot > erd.svg

Petr